Problem: A goblet contains $7$ red marbles, $6$ green marbles, and $6$ blue marbles. If a marble is randomly chosen, what is the probability that it is not green?
Solution: There are $7 + 6 + 6 = 19$ marbles in the goblet. There are $6$ green marbles. That means $19 - 6 = 13$ are not green. The probability is $ \frac{13}{19}$.